Importance Recently, a group of melanocytic tumors with loss of BAP1 expression has been described. The lesions may occur sporadically or as part of a familial cancer syndrome. They have distinct histopathologic features characterized by a nevuslike silhouette and cytologic composition of large epithelioid melanocytes with oval vesicular nuclei, distinct nucleoli, and abundant cytoplasm. The large melanocytes are immunohistochemically characterized by loss of nuclear labeling for BAP1.
Observations We describe a 21-year-old patient with multiple combined melanocytic proliferations composed of both a nevus component with strong BAP1 expression and a large epithelioid melanocyte population with loss of BAP1 expression. The occurrence of multiple BAP1loss melanocytic lesions raised concerns about a possible germline mutation. Sequence analysis of DNA from lesional and nonlesional skin confirmed a BAP1 germline mutation.
Conclusions and Relevance The presence of multiple clinically banal–appearing melanocytic lesions with childhood onset suggests that the combined lesions with BAP1loss large epithelioid melanocytes described herein are probably combined nevi. Our findings also illustrate how the detection of a histopathologically distinct melanocytic lesion, coupled with knowledge of its possible association with a hereditary tumor syndrome, can lead to the suspicion and confirmation of a germline mutation.